共查询到20条相似文献，搜索用时 125 毫秒
1.
Tidal residual eddies are one of the important hydrodynamic features in tidally dominant estuaries and coastal bays, and they could have significant effects on water exchange in a tidal system. This paper presents a modeling study of tides and tidal residual eddies in Puget Sound, a tidally dominant fjord-like estuary in the Pacific Northwest coast, using a three-dimensional finite-volume coastal ocean model. Mechanisms of vorticity generation and asymmetric distribution patterns around an island/headland were analyzed using the dynamic vorticity transfer approach and numerical experiments. Model results of Puget Sound show that a number of large twin tidal residual eddies exist in the Admiralty Inlet because of the presence of major headlands in the inlet. Simulated residual vorticities near the major headlands indicate that the clockwise tidal residual eddy (negative vorticity) is generally stronger than the anticlockwise eddy (positive vorticity) because of the effect of Coriolis force. The effect of tidal residual eddies on water exchange in Puget Sound and its subbasins was evaluated by simulations of dye transport. It was found that the strong transverse variability of residual currents in the Admiralty Inlet results in a dominant seaward transport along the eastern shore and a dominant landward transport along the western shore of the inlet. A similar transport pattern in Hood Canal is caused by the presence of tidal residual eddies near the entrance of the canal. Model results show that tidal residual currents in Whidbey Basin are small in comparison to other subbasins. A large clockwise residual circulation is formed around Vashon Island near entrance of South Sound, which can potentially constrain the water exchange between the Central Basin and South Sound. 相似文献
2.
Tarang Khangaonkar Brandon Sackmann Wen Long Teizeen Mohamedali Mindy Roberts 《Ocean Dynamics》2012,62(9):1353-1379
Nutrient pollution from rivers, nonpoint source runoff, and nearly 100 wastewater discharges is a potential threat to the ecological health of Puget Sound with evidence of hypoxia in some basins. However, the relative contributions of loads entering Puget Sound from natural and anthropogenic sources, and the effects of exchange flow from the Pacific Ocean are not well understood. Development of a quantitative model of Puget Sound is thus presented to help improve our understanding of the annual biogeochemical cycles in this system using the unstructured grid Finite-Volume Coastal Ocean Model framework and the Integrated Compartment Model (CE-QUAL-ICM) water quality kinetics. Results based on 2006 data show that phytoplankton growth and die-off, succession between two species of algae, nutrient dynamics, and dissolved oxygen in Puget Sound are strongly tied to seasonal variation of temperature, solar radiation, and the annual exchange and flushing induced by upwelled Pacific Ocean waters. Concentrations in the mixed outflow surface layer occupying approximately 5–20?m of the upper water column show strong effects of eutrophication from natural and anthropogenic sources, spring and summer algae blooms, accompanied by depleted nutrients but high dissolved oxygen levels. The bottom layer reflects dissolved oxygen and nutrient concentrations of upwelled Pacific Ocean water modulated by mixing with biologically active surface outflow in the Strait of Juan de Fuca prior to entering Puget Sound over the Admiralty Inlet. The effect of reflux mixing at the Admiralty Inlet sill resulting in lower nutrient and higher dissolved oxygen levels in bottom waters of Puget Sound than the incoming upwelled Pacific Ocean water is reproduced. By late winter, with the reduction in algal activity, water column constituents of interest, were renewed and the system appeared to reset with cooler temperature, higher nutrient, and higher dissolved oxygen waters from the Pacific Ocean. 相似文献
3.
Simulating the three-dimensional circulation and hydrography of Halifax Harbour using a multi-nested coastal ocean circulation model 总被引：2，自引：2，他引：0
Shiliang Shan Jinyu Sheng Keith Richard Thompson David Alexander Greenberg 《Ocean Dynamics》2011,61(7):951-976
Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world’s largest, ice-free natural
harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides,
flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development
of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct
the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for
2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated
with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent
observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also
compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour
over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm
surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical
processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal
currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine
circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of
this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner
Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in winter as expected
but it is also shown that a significant part of the temperature and salinity variability is driven by physical processes occurring
on the adjacent inner continental shelf, especially during storm and coastal upwelling events. 相似文献
4.
Fjord exchange circulation and its response to abrupt changes in forcing is examined by means of an idealized modeling experiment. Puget Sound, a fjord-type estuary in western North America (State of Washington), is the main context for this study. Parameters of the idealized model are representative of the entrance sill at Admiralty Inlet and the Main Basin of Puget Sound. Sensitivity to some of the model parameters relevant to a 3D realistic model is discussed. An idealized tidal forcing with fortnightly modulation drives a qualitatively realistic cycle of exchange circulation while the other boundary conditions are kept fixed in time. The cycle is characterized by fortnightly pulses of deep water intrusions with a sharp front at the leading edge and reversed circulation cells below the sill depth developing between the intrusions. This basic state is then perturbed and response of the circulation to abrupt changes in oceanic salinity and river discharge is examined. 相似文献
5.
Daniel J. Twigt Erik D. De Goede Firmijn Zijl Dirk Schwanenberg Alex Y. W. Chiu 《Ocean Dynamics》2009,59(6):1077-1093
Within the hydrodynamic modelling community, it is common practice to apply different modelling systems for coastal waters
and river systems. Whereas for coastal waters 3D finite difference or finite element grids are commonly used, river systems
are generally modelled using 1D networks. Each of these systems is tailored towards specific applications. Three-dimensional
coastal water models are designed to model the horizontal and vertical variability in coastal waters and are less well suited
for representing the complex geometry and cross-sectional areas of river networks. On the other hand, 1D river network models
are designed to accurately represent complex river network geometries and complex structures like weirs, barrages and dams.
A disadvantage, however, is that they are unable to resolve complex spatial flow variability. In real life, however, coastal
oceans and rivers interact. In deltaic estuaries, both tidal intrusion of seawater into the upstream river network and river
discharge into open waters play a role. This is frequently approached by modelling the systems independently, with off-line
coupling of the lateral boundary forcing. This implies that the river and the coastal model run sequentially, providing lateral
discharge (1D) and water level (3D) forcing to each other without the possibility of direct feedback or interaction between
these processes. An additional disadvantage is that due to the time aggregation usually applied to exchanged quantities, mass
conservation is difficult to ensure. In this paper, we propose an approach that couples a 3D hydrodynamic modelling system
for coastal waters (Delft3D) with a 1D modelling system for river hydraulics (SOBEK) online. This implies that contrary to
off-line coupling, the hydrodynamic quantities are exchanged between the 1D and 3D domains during runtime to resolve the real-time
exchange and interaction between the coastal waters and river network. This allows for accurate and mass conserving modelling
of complex coastal waters and river network systems, whilst the advantages of both systems are maintained and used in an optimal
and computationally efficient way. The coupled 1D–3D system is used to model the flows in the Pearl River Delta (Guangdong,
China), which are determined by the interaction of the upstream network of the Pearl River and the open waters of the South
China Sea. The highly complex upstream river network is modelled in 1D, simulating river discharges for the dry and wet monsoon
periods. The 3D coastal model simulates the flow due to the external (ocean) periodic tidal forcing, the salinity distribution
for both dry and wet seasons, as well as residual water levels (sea level anomalies) originating from the South China Sea.
The model is calibrated and its performance extensively assessed against field measurements, resulting in a mean root mean
square (RMS) error of below 6% for water levels over the entire Pearl River Delta. The model also represents both the discharge
distribution over the river network and salinity transport processes with good accuracy, resolving the discharge distribution
over the main branches of the river network within 5% of reported annual mean values and RMS errors for salinity in the range
of 2 ppt (dry season) to 5 ppt (wet season). 相似文献
6.
Forty-two surface sediment samples collected from the southern coastal East China Sea (ECS) were analyzed for organochlorine pesticides (OCPs). The results showed high concentrations of DDTs and parent DDT fractions in the nearshore area, suggesting that there is still a fresh input of these species from non-point sources, probably due to the recent usage of relevant products. However, for HCHs, the high concentrations with elevated β-HCH fraction were focused at the local major river estuaries, indicating that soils-released HCH input was mainly from the major river runoffs. The distribution and composition of OCPs in the coastal ECS could be more prominently controlled by the direct regional inputs rather than the general natural sorption process on particulate organic carbon. DDTs and chlordane are more important for their potential ecotoxicological risk on neighboring benthic community in the nearshore region and the local major river estuaries. 相似文献
7.
《Continental Shelf Research》2006,26(17-18):2319-2334
Instrumented bottom tripods have provided important data on sediment transport processes on continental shelves and in estuaries for four decades. Since the initial deployment in a tidal channel in Puget Sound, WA, in 1965 numerous tripods have been constructed to investigate bottom boundary layer and sediment dynamics worldwide. Tripod data have led to new understanding of near-bottom wave and current flows in the coastal ocean, and have been crucial to the development of shelf circulation and sediment transport models. Calculations of bottom stress, bottom roughness, and sediment flux that resulted directly from tripod data have been compared to bottom boundary layer model results. Where these have differed, new or revised model components have been developed to improve the skill of the models. The many discoveries that have been made from tripod experiments include dense, near-bottom fluid mud layers that transport large quantities of suspended sediment offshore into deeper regions of the continental shelf. This process has been linked to the seaward progradation of subaqueous deltas and to the boundaries of mid-shelf mud deposits off rivers with high fine-sediment discharge. 相似文献
8.
The response of the Chesapeake Bay to river discharge under the influence and absence of tide is simulated with a numerical model. Four numerical experiments are examined: (1) response to river discharge only; (2) response to river discharge plus an ambient coastal current along the shelf outside the bay; (3) response to river discharge and tidal forcing; and (4) response to river discharge, tidal forcing, and ambient coastal current. The general salinity distribution in the four cases is similar to observations inside the bay. Observed features, such as low salinity in the western side of the bay, are consistent in model results. Also, a typical estuarine circulation with seaward current in the upper layer and landward current in the lower layer is obtained in the four cases. The two cases without tide produce stronger subtidal currents than the cases with tide owing to greater frictional effects in the cases with tide. Differences in salinity distributions among the four cases appear mostly outside the bay in terms of the outflow plume structure. The two cases without tide produce an upstream (as in a Kelvin wave sense) or northward branch of the outflow plume, while the cases with tide produce an expected downstream or southward plume. Increased friction in the cases with tide changes the vertical structure of outflow at the entrance to the bay and induces large horizontal variations in the exchange flow. Consequently, the outflow from the bay is more influenced by the bottom than in the cases without tide. Therefore, a tendency for a bottom-advected plume appears in the cases with tide, rather than a surface-advected plume, which develops in the cases without tide. Further analysis shows that the tidal current favors a salt balance between the horizontal and vertical advection of salinity around the plume and hinders the upstream expansion of the plume outside the bay. 相似文献
9.
Regularities in the diurnal variations of hydrochemical characteristics in the coastal zone of a sea
O. V. Shevtsova 《Water Resources》2009,36(3):325-336
Amur Bay (Sea of Japan) is used as an example to show that the range of diurnal variations of hydrochemical characteristics in the coastal zone of a sea subject to the effect of continental runoff features some regularities. Specifically, variations of water salinity in the surface frontal zone of estuaries exponentially increase toward the river and reach the largest magnitude in the zone of high longitudinal gradients, where diurnal salinity distributions are found to deviate from the normal law. 相似文献
10.
A three‐dimensional, time‐dependent hydrodynamic and salinity model was applied to the Danshuei River estuarine system and adjacent coastal sea in Taiwan. The model forcing functions consist of tidal elevations along the open boundary and freshwater flows from the main stem and tributaries in the Danshuei River system. The bottom roughness height was calibrated and verified with model simulation of barotropic flow, and the turbulent diffusivities were calibrated through comparison of time‐series of salinity distributions. The overall model verification was achieved with comparisons of residual current and salinity distribution. The model simulation results are in qualitative agreement with the available field data. The model was then used to investigate the tidal current, residual current, and salinity patterns under the low freshwater flow condition in the modelling domain. The results reveal that the extensive intrusion of saline water imposes a significant baroclinic forcing and induces a strong residual circulation in the estuary. The downriver net velocity in the upper layer increases seaward despite the enlargement of the river cross‐section in that direction. Strong residual circulation can be found near the Kuan‐Du station. This may be the result of the deep bathymetric features there. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
11.
The response of the electric and magnetic field variations over the San Juan Bay region of Vancouver Island is studied using a scaled laboratory analogue model. The laboratory frequencies simulate periods of 10 and 100 s in the geophysical problem. The model results indicate that, for both E- and H-polarization of the source field, induced current in the ocean is deflected around Cape Flattery and channelled into the Juan de Fuca Strait. With increasing period, the proportion of current channelled into the Strait decreases sharply. Induced current in the strait is also funnelled into San Juan Bay, a finger-shaped bay ca. 4 km wide and 7.5 km long, for both polarizations of the source field. The effect of the Bay on the field response is confined to the local region, within approximately 6 km of the centre of the Bay. Good agreement between field station and analogue model Hz results was obtained for the San Juan Bay. The behaviour of the Parkinson arrow for these two stations is examined with the aid of the analogue model results. 相似文献
12.
Freshwater inflow is central to the definition of estuaries and if we lose control of the quantity of freshwater flow or discharge (including seasonal timing) to estuaries, then freshwater water quality has the potential to become a moot issue in estuarine ecosystems (Definition of estuaries: estuaries (aestus = tide) are physico-chemically, geomorphically, and biotically diverse ecosystems. Although numerous definitions of estuaries exist, we prefer the following: an estuary is a partially enclosed coastal water body in which freshwater runoff, often seasonally and episodically pulsed, dilutes salty ocean water and the biotic structure is influenced by dynamic tidal action and associated salinity gradients and reef building organisms and wetlands influence development and evolution of ecological structure and function (see for expanded definition)). 相似文献
13.
A high-resolution coastal ocean model was developed to simulate the temporal/spatial variability of the Kennebec–Androscoggin
(K–A) river plume and the circulation in Casco Bay. The model results agree favorably with the moored and shipboard observations
of velocity, temperature, and salinity. The surface salinity gradient was used to distinguish the plume from the ambient coastal
water. The calculated plume thickness suggests that the K–A plume is surface trapped. Its horizontal scales correlate well
with Q
0.25, where Q is the volume discharge of the rivers. Directional spreading is affected by the wind with the upwelling favorable wind transporting
the plume water offshore. Both the wind and the tide also enhance mixing in the plume. The inclusion of a wetting-and-drying
(WAD) scheme appears to enhance the mixing and entrainment processes near the estuary. The plume becomes thicker near the
mouth of the estuary, the outflow velocity of the plume is weaker, and the radius of the river plume shrinks. The flow field
in the model run with the WAD is noisier, not only in shallow areas of Casco Bay but also in the plume and even on the shelf.
We speculate that the WAD processes can affect much larger areas than the intertidal zones, especially via a river plume that
feeds into a coastal current. 相似文献
14.
Electromagnetic induction in the Vancouver Island region for a uniform inducing source field for 300 s period is investigated with the aid of three-dimensional (3-D) numerical and analogue model results and field site measurements. The thin sheet numerical model, based on the subducting Juan de Fuca plate analogue model ofDosso
et al., consists of a 5km thick non-uniform thin sheet (comprising the lateral conductivity contrasts arising from the land, the varying depth ocean, and the sediment) underlain by a four-layer conductive structure. The four-layer conductive structure beneath the non-uniform thin sheet simulates the effect of the Juan de Fuca plate subducting Vancouver Island. To examine the effects of the ocean channel depth between Vancouver Island and the British Columbia (Canada) mainland, numerical results were obtained for two channel depths (0 and 600 m). The results indicate that the channel plays an important role in the geomagnetic response in the central and inner coastal regions of Vancouver Island. The general agreement of the 3-D numerical model induction arrows with the analogue model and field site induction arrows for 300 s supports the premise of a layered conductive substructure dipping at a small angle, at most, beneath Vancouver Island.Lithoprobe Publication No. 311. 相似文献
15.
Measurements of geomagnetic induction responses for a laboratory analogue model, that includes a simulation of the subducting Juan de Fuca Plate, are compared with those obtained at three sites on Vancouver Island. Good agreement between model and field responses at the central Vancouver Island site is observed over the period range 3–60 min, while at the east and west coastal sites, good agreement is achieved only for periods greater than 20 min. At shorter periods, departures of the observed responses from those of the model are possibly the result of upper crust inhomogeneities not replicated in the simulation, and the complex strait with its numerous small islands and its irregular coastlines inadequately simulated in the course model. Nevertheless, the analogue model results are consistent with the premise of a Juan de Fuca plate, underlain by the conductive asthenosphere, subducting at a shallow depth beneath Vancouver Island. 相似文献
16.
《水文科学杂志》2013,58(3):441-454
Abstract In wells tapping coastal aquifers, piezometric fluctuations can be observed in response to the ocean tide. Simultaneous recordings of the ocean tide and of the piezometric variations may provide a basis for characterizing the hydrodynamics of the aquifer. This approach was attempted to characterize the Dridrate aquifer, located on the Atlantic coast of Morocco. This aquifer accounts for most of the regional drinking water resources. However, its hydrodynamic characteristics are very poorly known. The study compares observed and simulated piezometric fluctuations, under various assumptions (confined, semi-confined aquifer). The model, which best explains the hydrodynamic behaviour of this aquifer is a semi-confined and strongly heterogeneous aquifer model (calculated hydraulic diffusivity values vary over several orders of magnitude). This result is new and rather surprising, since to date this aquifer was considered confined in view of its geological setting. Consequently, new questions are raised regarding the protection and management of the groundwater resources of this aquifer. 相似文献
17.
Seasonal circulation of the Bohai Sea (BS) in 1992 was investigated using Lagrangian particle tracking method. The hydrography
of the BS was simulated based on an unstructured grid, finite-volume, three-dimensional primitive equation ocean model. With
the use of the unstructured triangular grid, the model can easily fit the irregular coastal boundary of the BS. The simulated
tides, tidal current, and thermohaline field agreed well with the observations. The transport of particles has three-dimensional
structure in the BS. Compared with central Bohai and Bohai Strait, the differences of particles’ transportation between surface
and bottom layer in three bays are small. The circulation in the summer is stronger than that in the winter, with the average
residual velocity in the surface layer being about 3.7 cm/s during the summer while only 1.8 cm/s during the winter. Using
the same model, several well-designed numerical experiments were performed to investigate the effect of oceanic tide, river
discharge, wind stress, and thermal stratification on the circulation. It is shown that winds play an important role in the
circulation of the BS during both the winter and the summer. Density circulation is important during the summer; however,
it is negligible during the winter. River runoff only affects the area around the river mouth. Compared with wind and thermohaline
effect, the contribution of tides is small during the summer, and the circulation under only M2 tidal constituent could not reflect the actual circulation of the BS. 相似文献
18.
H.W. Dosso W. Nienaber J.A. Wright J.P. Greenhouse R.C. Bailey 《Physics of the Earth and Planetary Interiors》1980,23(1):13-30
The behavior of electric and magnetic field variations over the eastern coastal region of North America is studied using a scaled laboratory electromagnetic analogue model. The model source frequency used simulates a period of 1 h in the geophysical scale. The results indicate that deflection and conductive channelling of induced electric current is important for both the E-polarization (northeast-southwest direction of the electric field of the source) and the H-polarization (northwest-southeast) of the source field. In the model, conductive channelling occurs through the Strait of Belle Isle, Cabot Strait, and in the St. Lawrence River. Current deflection is particularly prevalent around the southeast coast of Newfoundland for both E- and H-polarization, and around the northeast coastline of Nova Scotia for E-polarization. The model results also show current deflection by cape and bay coastal features, as well as by ocean depth contours.A comparison of model measurements for the cases of a uniform source field and a line current source indicate that the nature of the source field has a measurable but surprisingly small effect on the vertical to horizontal magnetic field ratio for both E- and H-polarizations, and negligible effect on the magnetotelluric ratio for coastal regions.The model fields in coastal regions were found to be strongly influenced by induced currents, deflected and channelled by the coastline and ocean bathymetry, and were dependent on the nature and particularly the polarization of the source field. Thus, along the complex coastline of eastern North America, a wide range of electric and magnetic field values should be expected. In some regions the coast effect, measured by the vertical to horizontal magnetic field ratio at the coast, could be expected to be extremely small or absent, while in other regions the ratio could approach a value as large as unity for variations of 1 h period. 相似文献
19.
Employing clean and quantitative techniques, a marine monitoring programme succeeded in detecting large surface elevations in the concentrations of dissolved Cu, Zn and Pb in the marine surface waters of Puget Sound adjacent to Seattle and Tacoma, Washington. Physical mixing with cleaner waters was the controlling factor in reducing the dissolved concentrations of Cu downstream of these contaminated regions. Comparisons between Puget Sound waters and coastal waters adjacent to Puget Sound suggest that a portion of this Cu, Zn and Pb pollution is being advected out of Puget Sound. The low Ni and Cd concentrations found in this study indicate that these trace metals are not a significant pollution problem in the main basin of Puget Sound. 相似文献
20.
The local subduction geometry at a site south of Puget Sound in western Washington is investigated using teleseismicP-waveforms recorded on a three-component event triggered seismograph. The data are processed using source equalization deconvolution in order to isolate locally convertedP-to-S arrivals and stacked to improve the signal-to-noise ratio. Stable arrivals in the radial component indicate an oceanic Moho within the subducted slab at a depth of about 53 km beneath the station. Observed amplitude variations with azimuth in the radial data, as well as qualitative aspects of the tangential data, are used to establish a slab dip of 16° to the southeast. Our results are compatible with previous results from a site 60 km to the west, and further confirm a substantial warp in the regional geometry of the subducted Juan de Fuca plate. 相似文献